1. Field of the Invention
The present invention relates to a display device that displays images by current-driving light emitting devices provided with respect to each pixel. Specifically, the invention relates to a so-called active matrix type-display device that controls amounts of current to be applied to light emitting devices such as organic EL devices with insulated gate field effect transistors provided within the respective pixel circuits. Further, the invention relates to electronic equipment in which such a display device is incorporated.
2. Background Art
In a display device such as a liquid crystal display, many liquid crystal pixels are arranged in a matrix form, and images are displayed by controlling transmittance intensity or reflectance intensity of incident light according to image information to be displayed with respect to each pixel. The same applies to an organic EL display using organic EL devices as pixels, however, the organic EL devices are self-luminous devices unlike the liquid crystal pixels. Accordingly, the organic EL display has advantages that the image visibility is higher, no backlight is necessary, and the response speed is faster in comparison to the liquid crystal display. Further, brightness levels (gradation) of the respective light emitting devices are controllable with amounts of current flowing therethrough, and the organic EL display is a so-called current control type device and largely different from voltage control type devices like the liquid crystal display.
In the organic EL display, there are drive systems of a simple matrix system and an active matrix system as is the case of the liquid crystal display. The former is simple in structure, however, it has problems in difficulty of realizing a large-scaled and high-definition display etc., and currently, the active matrix type system is increasingly developed. This system is to control the current flowing in the light emitting devices within the respective pixel circuits with active elements (generally, thin-film transistors, TFTs) provided within the pixel circuits, and disclosed in JP-A-2003-255856 (patent document 1), JP-A-2003-271095 (patent document 2), JP-A-2004-133240 (patent document 3), JP-A-2004-029791 (patent document 4), and JP-A-2004-093682 (patent document 5).